Oct. 11 (UPI) -- As millions of birds migrate south for the winter, many face dangerous obstacles on their journey, and experts say people can help them have a safe trip. This week saw the biggest migration event ever recorded by the BirdCast , a bird study project at Cornell University in Ithaca, N,Y. -- 1.25 billion. Farther south, trackers at Virginia Tech University report more than 36 million birds have already migrated this fall. But while these flights are an incredible natural event,